Presently, although the outer contour of the telescopic unit is generally square, since there does not have to be relative rotation between both, in some cases the inside section of the outside body and the outside contour of the inside body is circular, which implies a subsequent assembly of the diametric projections of the firing hammer, which is carried out by means of an insertable pin which is introduced in a diametric hole of the hammer, this operation must be carried out after the introduction of the firing hammer, simultaneously to the compression effected on the springs which aid the firing hammer and the telescopic unit. The assembly of this pin considerably increases the manufacturing costs of the piece itself and those of assembly of the mechanism.
Other present devices foresee a section different from the circular one in the outside and inside contour respectively in order to permit the introduction of a firing hammer which has the radial projections obtained simultaneously with it, but due to the fact that it has to be rotated in another position in which these projections are retained in the wall of said body and emerge through the windows existing in the other telescopic body, this all leads to a notable cost increase in the obtainment of some unsymmetric forms and therefore difficult to mold. These last present devices are inherently difficult to assemble due to the fact that all the components have to be coupled in a single direction, without partial assembles being previously effected. Besides, upon the outside telescopic body being where the springs are located, the body being of a single piece, the material has to be conducting which makes the product more expensive.